Removal and Reconstruction of the Gabion Weir at the Cantua Creek Harlan Drain Inlet Project

Removal and Reconstruction of the Gabion Weir at the Cantua Creek Harlan Drain Inlet Project

Due to damages to the existing gabion weir at the inlet, Department of Water Resources San Luis Field Division (SLFD) must remove the gabion weir and construct a new one. The gabion weir was designed to control Cantua Creek water and sediment before it enters the California Aqueduct (Aqueduct) through the inlet. An erosion in the Aqueduct embankment that occurred when the gabion weir was damaged must also be repaired. SLFD personnel and SLFD’s Engineering Branch will conduct the work; the California Conservation Corps may assist. The new gabion weir will conform to the design specifications of the original one. The gabion weir walls are made of rock filled gabions that are stacked and tied together; the foundation of the gabion weir is made of rock filled reno mattresses. The inlet contains two wing walls that are made of concrete. Figure 2 contains diagrams of these structures. To prepare the work area, an excavator will be operated from alongside the existing gabion weir to clear the gabion weir and inlet of sediment, vegetation, and debris. The removed vegetation will be relocated to one of the existing spoil areas. Removed trash or other debris will be disposed of at an appropriate off site location. Removed sediment that can be used as backfill for the new gabion weir, or that can be used to repair erosions in the Aqueduct embankment near the inlet, will be stockpiled near the gabion weir. Sediment that is not needed will be added to the existing protection levee north of the gabion weir and west of the Aqueduct embankment. Once the sediment, vegetation, and debris are removed, a temporary concrete-block wall will be installed to prevent Aqueduct water from entering the work area through the inlet. An excavator will create a flat surface from the end of one inlet wing wall to the end of the other wing wall, and 6-foot-long, by 2-foot-tall, by 2-foot-wide concrete blocks will then be placed between the wing walls to form the temporary wall. The temporary wall will measure approximately 6 feet high, 36 feet long, and 2 feet wide. After it is constructed, any water remaining in the work area will be pumped back into the Aqueduct. The remaining work will be performed after the water is removed from the work area. Approximately 200 cubic yards of sediment will be excavated to uncover the gabion weir and underlying reno mattresses. On both sides of the inlet, approximately 15 feet of Aqueduct embankment will be excavated to uncover the portions of the gabion weir that are built into it. When the gabions and reno mattresses are uncovered, they will be dismantled and removed from the gabion weir structure by disconnecting them from one another using hand tools and equipment. A backhoe or excavator will place the gabions and reno mattresses on the ground, where they will be opened and the rocks inside the cages can be removed and sorted. Rocks that can be used to fill the new gabions and reno mattresses will be left on site; rocks that cannot be used will be removed and disposed of at an appropriate off site location. If additional rocks are needed, up to 30 tons would be imported. The old wire caging will be taken off site and disposed of at an appropriate location. SLFD’s Engineering Branch will establish the grade for the new reno mattress footing. Approximately 20 cubic yards of soil will be removed, and the area will be contoured and compacted to establish the grade to original design specifications. The graded footing will be lined with geotextile fabric. New reno mattress wire cages will be placed on top of the geotextile fabric and will provide the foundation for the new gabion weir. The reno mattress cages will be filled with rocks and tied together; each completed reno mattress will be about 9 inches tall, 6 feet wide, and 9 feet long. Reno mattresses will be assembled until there are enough to meet the original foundation design specifications. New gabion cages will be placed on top of the filled reno mattresses, filled with rocks, and tied together. The tied gabions will be about 3 feet tall. Gabions will be assembled until there are enough to meet the original design specifications for the gabion weir. When construction of the new gabion weir is completed, the eroded Aqueduct embankment north of the inlet will be backfilled and compacted until the embankment is returned to design specifications; the area surrounding the gabion weir will be contoured and compacted to design specifications, and the temporary wall will be removed. The State Water Project will benefit from this work

Fresno

Southern California